Two step synchronization procedure for orthogonal frequency division multiplexing (OFDM) receivers

• US 20040105512A1
• Filed: 12/02/2002
• Published: 06/03/2004
• Est. Priority Date: 12/02/2002
• Status: Abandoned Application

• Current Assignee: Nokia Corporation
• Original Assignee: Nokia Corporation
• Inventors: Priotti, Paolo
• Application Number:
  US10/307,743
• Publication Number:
  US 20040105512A1
• Time in Patent Office: Days
• US Class Current: 375/340
• CPC Class Codes: H04L 1/0618 Space-time coding
• CPC Class Codes: H04L 25/0212 of impulse response
• CPC Class Codes: H04L 25/0224 using sounding signals
• CPC Class Codes: H04L 27/2657 Carrier synchronisation
• CPC Class Codes: H04L 27/2662 Symbol synchronisation
• CPC Class Codes: H04L 27/2665 Fine synchronisation, e.g. by positioning the FFT window

Abstract

A method is disclosed to determine fine time synchronization in an OFDM digital receiver, as is receiver that operates in accordance with the method. The method includes buffering in a buffer normalized auto-correlation values derived from received OFDM signal samples and processing the buffered values by selecting first synchronization instants using a first selection window having a width of j samples, and selecting second synchronization instants using a second selection window having a width of k samples, where k<j, and where the second selection window is centered on an average timing computed as a result of the processing that occurred using the first selection window. In a preferred but non-limiting embodiment of this invention j=96 samples and k=16 samples. The buffering step includes first auto-correlating received signal samples to generate correlation peaks corresponding ideally only to cyclic prefix fields occurring within a received OFDM packet, normalizing the correlation peaks as a function of signal energy and storing signal samples in the buffer memory that include samples that correspond to the normalized correlation peaks. The OFDM receiver may form a part of a Multiple-Input, Multiple Output (MIMO) receiver that has a plurality of receive antennas. In this case the steps of buffering and processing occur in parallel for each of the plurality of receive antennas.

Claims

1. A method to determine fine time synchronization in an Orthogonal Frequency Division Multiplex (OFDM) digital receiver, comprising:

buffering a plurality of auto-correlation values corresponding to a signal received from an OFDM transmitter; and

processing the buffered auto-correlation values by selecting first synchronization instants using a first selection window having a width of j samples, and selecting second synchronization instants using a second selection window having a width of k samples, where k<

j, and where the second selection window is centered on an average of synchronization timing instants determined as a result of the processing that occurred using the first selection window.

2. A method as in claim 1, where buffering comprises normalizing the plurality of auto-correlation samples, and storing the normalized auto-correlation values in a memory.

3. A method as in claim 1, where j=96 samples and k=16 samples.

4. A method as in claim 1, where buffering comprises first auto-correlating received signal samples to generate correlation peaks corresponding, ideally, only to cyclic prefix fields occurring within a received OFDM packet.

5. A method as in claim 1, where buffering comprises first auto-correlating received signal samples to generate correlation peaks corresponding, ideally, only to cyclic prefix fields occurring within a received OFDM packet, normalizing the correlation peaks as a function of signal energy, and storing the normalized auto-correlation values in a buffer memory.

6. A method as in claim 1, where the receiver comprises a Multiple-Input, Multiple Output (MIMO) receiver having a plurality of receive antennas, and where steps of buffering and processing occur in parallel for each of the plurality of receive antennas.

7. An Orthogonal Frequency Division Multiplex (OFDM) digital receiver, comprising:

a memory for buffering a plurality of auto-correlation values corresponding to signals received from an OFDM channel; and

circuitry for processing the buffered auto-correlation values to select first synchronization instants using a first selection window having a width of j samples, and to select second synchronization instants using a second selection window having a width of k samples, where k<

j, and where the second selection window is centered on an average of synchronization timing instants determined as a result of the processing that occurred using the first selection window.

8. An OFDM receiver as in claim 7, where j=96 samples and where k=16 samples.

9. An OFDM receiver as in claim 7, further comprising circuitry, having an output coupled to said memory, for auto-correlating received signal samples to generate correlation peaks corresponding, ideally, only to cyclic prefix fields occurring within a received OFDM packet.

10. An OFDM receiver as in claim 7, further comprising circuitry, having an output coupled to said memory, for auto-correlating received signal samples to generate correlation peaks corresponding, ideally, only to cyclic prefix fields occurring within a received OFDM packet, for normalizing the correlation peaks as a function of signal energy, and for storing normalized auto-correlation values in said memory.

11. An OFDM receiver as in claim 7, where said receiver comprises a Multiple-Input, Multiple Output (MIMO) receiver having a plurality of receive antennas, and where there is an instance of said memory and processing circuitry for each of said plurality of receive antennas.

12. A method to determine fine time synchronization in an Orthogonal Frequency Division Multiplex (OFDM) digital receiver, comprising:

auto-correlating and normalizing received signal samples from an OFDM packet to generate normalized auto-correlation values have peak values corresponding, ideally, only to cyclic prefix fields occurring within the received OFDM packet;

storing the normalized auto-correlation values in a buffer; and

processing the buffered normalized auto-correlation values by selecting first synchronization instants using a first selection window having a width of j samples and selecting second synchronization instants using a second selection window having a width of k samples, where the second selection window is centered on an average of the synchronization instants determined as a result of the processing that occurred using the first selection window.

13. A method as in claim 12, where a result of the processing that occurs using the second selection window is to generate a synchronization vector that is input to a data alignment and guard interval removal block that thereafter outputs pilot signals, time-synchronized data and training symbols.

14. A method as in claim 12, where the signal samples that are auto-correlated are expressed using variable quantization.

15. A method as in claim 12, where the signal samples that are auto-correlated are expressed using three bit quantization.

16. A method as in claim 12, where the receiver comprises a Multiple-Input, Multiple Output (MIMO) receiver having a plurality of receive antennas, and where steps of storing and processing occur in parallel for each of the plurality of receive antennas.

17. A method as in claim 16, where the determined timing is averaged among the plurality of receive antennas to yield a single reference timing.